1. Field of the Invention
The present invention relates generally to power control and, more particularly, to controlling power to processors, such as graphics processing units.
2. Description of the Related Art
In computer systems with multiple processors, power is continuously supplied to each of the processors even though one or more of the processors are idle. This results in unnecessary power consumption because of chip leakage, use of extra local memory and an additional intermediary bus, dedicated voltage regulation, and cooling. The chip leakage problem is expected to worsen as chip's silicon process geometry continues to shrink to allow the chip's operating clock frequency to increase.
One example of a computer system with multiple processors is one that employs a discrete graphics adapter card. In this computer system, there is one GPU on a motherboard or integrated with a central processing unit (CPU), and another GPU on the discrete graphics adapter card. Typically, the GPU on the card is faster and has better display capabilities. However, the GPU on the discrete graphics adapter card causes an increase in power consumption of the overall system, even when it is idle, for the aforementioned reasons.
A GPU on a discrete graphics adapter card is normally powered through voltage supply rails of the card, and turning off the power to the card is difficult for several reasons. First, the voltage supply rail to the discrete graphics adapter card needs to be separated from the voltage supply rails to other cards since expansion card slots normally share voltage supply rails. Second, expensive high-current and/or fast-switch devices need to be implemented to provide on/off power control for the discrete graphics adapter card. This functionality cannot be provided by existing components, namely the computer system power supply, because the computer system power supply do not provide on/off control except for the whole system.
Current computer systems employ means to control power to CPUs and GPUs in order to support various sleep states. For example, notebook computers have used controllers, such as an embedded controller or a keyboard controller, and system software in order to support sleep states of the GPU such as suspend and low power D3-cold. However, even when a processor is in a sleep state, power is still consumed and, for higher performance processors, chip leakage becomes substantial.